1. Field of the Invention
This invention relates to an exhaust duct cleaning system. More particularly, this invention relates to a cleaning system for use in an exhaust duct of a cooking unit in which the system is permanently installed in the exhaust duct and is operated on an automatic time cycle. The system is particularly designed for use in commercial establishments such as restaurants where the cooking facilities are used continuously so that grease buildup becomes a problem in the exhaust duct.
2. Description of the Prior Art
There is a wide variety of equipment available on the market for cleaning exhaust ducts and hoods in restaurants and other cooking establishments.
The vast majority of exhaust systems are cleaned on an unscheduled basis, usually when the grease and sludge buildup has become so great that it affects proper ventilation or has become a fire or health hazard. Most of the cleaning is done by hand using long-handled scrapers, and the entire process is a dirty, messy job. The cleaning must be done in the restaurant off hours, and the effectiveness of such cleaning often leaves much to be desired. A good employee on this job usually has a short tenure.
The use of commercial cleaning companies also has many drawbacks. Again, the job must be done during off hours, and problems associated with grease buildup are often exasperated by only scheduling cleaning "when needed." Commercial cleaning can be more effective than normal in-house cleaning because of the use of special equipment such as steam cleaning guns and the like, but extreme care has to be exercised by experienced personnel so as not create other hazards such as grease and water on floors and clogged drains.
Various attempts have been made to install equipment permanently in the hoods and ducts. A common technique is to employ baffles to create a tortuous or zigzag air path above the hood so that the grease-laden air travelling through the path or channels deposits the grease on the baffles to be removed by a water spray. The channels and water spray can be integrally mounted in the duct, or the zigzag channel portion can be supplied as part of a removable cartridge for spray or immersion cleaning when the cartridge is removed from the exhaust system. Many problems are associated with this type of equipment, not the least of which is the increased pressure drop experienced and the increased fan size required.
Other systems utilize spray nozzles at strategic locations within the exhaust duct pointed at given spots in the duct or at particular baffling, which systems depend primarily on the gravity flow downward of the cleaning liquid to perform the primary cleaning function rather than the energy of impinging jets.
Other systems utilize a nozzle pipe which extends along the axis of the exhaust duct so as to disperse the spray along a major part of the length of the duct. Some of these longitudinally extending pipes also have been caused to rotate so as to spray around the interior perimeter of the exhaust pipe. However, the difficulty with both of these systems is that the spray must travel a considerable distance before it impinges upon the wall of the duct, thus losing energy, and they invariably do not cover the entire area with direct impingement. While rotation of the nozzle pipe can aid to some extent, it will only approximate circumferential coverage in a round duct configuration and will be totally inadequate in a rectangular duct.
A further improvement in the rotating nozzle pipe configuration has been to branch off from the axis of the exhaust duct to bring the pipe closer to the inner periphery of the exhaust duct as it is rotated. While this improves the efficacy of a round exhaust duct system, it still does not insure longitudinal coverage, and aggravates a situation where the duct cross-section is rectangular.